Varying vulnerabilities: Seagrass species under threat from prolonged ocean warming

Abstract

Understanding the response of various seagrass species to prolonged elevated water temperatures is crucial for effective management and seagrass species restoration amid increasing climate change‐induced ocean warming and marine heat waves. This is especially important in intertidal seagrass meadows, where heat can penetrate substrate depths of up to 50 cm. We assessed and contrasted the responses of five intertidal species—Zostera muelleri Irmisch ex Asch, Halophila ovalis (R.Br.) Hook f., Halodule uninervis (Forssk.) Asch, Halophila decipiens Ostenf., and Halophila spinulosa (R.Br.) Asch—over a month of elevated temperatures by examining rhizome growth, number of living shoots, root development, and sprig survival. While all the species appeared to negatively respond to elevated water temperatures, our results indicate notable interspecific variations in their reactions to prolonged warming stress. Two Halophila species, including H. ovalis and H. spinulosa, are sensitive to prolonged heat stress exceeding 10°C above ambient. Halodule uninervis is the most tolerant of elevated water temperature, followed by Zostera muelleri, although the latter is still negatively affected. Intertidal H. decipiens appears to be highly vulnerable to disturbance and performs poorly in mesocosm settings. This study offers an initial understanding of how climate change might impact these seagrass species, whose ecological functions are not easily replaceable once lost.